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Consciousness has recently become a hot topic. The subject of increasingly arcane debates among philosophers of mind two decades ago, it now also commands the interest of some of the leading thinkers and researchers in fields as diverse as neuroscience, linguistics, psychology, artificial intelligence and cognitive science. The Journal of Consciousness Studies has emerged, while Roger Penrose and Stuart Hameroff's seemingly batty ideas about quantum consciousness and the role of microtubules turned into a best-selling book.

What is perhaps disappointing is the relative impoverishment of the conceptual framework within which this flurry of activity is being pursued. Almost everyone rejects the old Cartesian substance dualism in which mind and matter are incommensurable. We are all apparently physicalists, or at least monists, these days, and so for most of the disputants the question becomes one of solving "the hard problem" of how "objectively" observable neurobiological facts about brain processes can generate "subjective" experiences. The possibility that such experiences are not "generated" by brain (and body) processes, but are no more and no less than another way of describing the same phenomena, is apparently not acceptable, though I have never been quite clear why. So we are back with one old debate, as to whether my experience of seeing red is the same as yours, and one new one, as to how and why did consciousness evolve - that is, what function, in an intellectual landscape dominated by Darwinian metaphors, does it subserve? The first question has always struck me as not merely unanswerable, but vacuous. The answer to the second seems obvious: human consciousness, however defined, has contributed to the evident - to date - evolutionary success of our species, and cannot therefore be epiphenomenal. Being conscious, whatever we mean by it, must be a consequential function of our biological organisation as members of a species of social individuals with large brains and communication skills. But the argument that consciousness is not merely the obverse of unconsciousness, that it is not some static brain/mind process but rather a socially, historically, developmentally engendered statement about the relationship between an individual and the surrounding world, cuts little ice - perhaps because the discussion is still being conducted primarily between philosophers trained in the classical mode and neuroscientists, and thus excludes the social and historical domains.

Of such philosophers, Colin McGinn is one of the more entrenched examples. His book is an encapsulation of a position that he has described as the new mysterianism. Both materialists and dualists are asking the wrong sort of question, he argues, so it is not surprising they get the wrong answers. Consciousness, for McGinn, is the ultimate mystery. Perhaps we are as a species simply not intelligent enough to solve the problem? How can meat be sentient? How can any complex ensemble of cells generate consciousness? It cannot, he asserts. After all, neither kidneys nor galaxies are conscious despite their complexity, and hence there is an unbridgeable gulf between brain and mind. However closely one observes neurons or records their activity with imaging techniques, one will only ever observe correlates of consciousness, not consciousness.

Well yes, but equally, however closely one observes the protein filaments of actin and myosin sliding across one another, one will never "observe" muscular contraction, merely a correlate of muscular contraction. Yet we have no doubt that the two observations, of sliding filaments observed biochemically and muscle contraction observed physiologically, are actually observations of the same phenomenon, but at different levels of analysis or described within different discourses. And the analogy with galaxies simply does not hold. The point about brains is not merely that they contain a lot of cells, but that these cells are connected by an even larger number of synapses (up to a thousand trillion) whose potential patterns have more permutations than there are particles in the known universe, and whose connectivity is dynamically developed through the long drawn-out process of ontogeny, making possible the encoding of our own personal as well as our species' histories. Neither galaxies nor kidneys possess such properties. There are no mysteries there - at least none in the McGinn sense, and if only he could relax a bit and recognise that it might be better to regard consciousness as a process rather than a thing, he might release the hook on which he is impaled. The trouble is that McGinn's book is a compilation of ex cathedra assertions about what is or is not possible or believable. I have no compunction about making, possibly with equal lack of evidence, contrary assertions, but clarity is not advanced by obiter dicta .

All of which makes it a pleasure to experience Antonio Damasio's very different approach. He is a neurologist who, with his partner Hanna, has pioneered brain-imaging techniques in the study of neuropsychological damage. His previous book, Descartes' Error (1996), was a convincing plea to transcend the computer-dominated, information-processing metaphor within which much cognitive neuroscience is embedded and to recognise the central organising role of emotion in understanding both the workings of our own brains and minds, and their evolutionary history. The Feeling of What Happens builds on the ideas of the earlier book in approaching the question of consciousness, and the result is unequivocally one of the two best books on the theme yet written by a neuroscientist (the other being neurophysiologist Walter Freeman's How Brains Make up their Minds (1999)). Both go further than any other neuroscientist towards recognising the significance of the social and insisting that naive reductionism is simply not sufficient, and that the debates over consciousness cannot be confined to cosy interchanges between biologists and traditional philosophers of mind.

Damasio insists that brains are embedded in bodies. Thus simple neuronal connectivity is insufficient to account for how they function; neurons are bathed in neurohormones and neuromodulators that are generated in response to surges in body hormones and in turn profoundly affect states of consciousness. Consciousness, "the feeling of knowing" as he puts it, is an evolved property, and hence varying forms and degrees of consciousness can be found among species that share a common evolutionary history with humans. He distinguishes between what he calls core and extended consciousness. The former is a common stable property of many animals, the ability, as he puts it, to be aware of the present moment, and, dimly, of the immediate past without illuminating the future. The latter is organisationally far more complex and develops over a lifetime. It engages memory and communication skills and enables a sense of the future to emerge; it too is not exclusively human but a capacity we share with our closer species relatives. With extended consciousness comes the beginning of a sense of self - proto-self. Finally, and this is the exclusively human consequence of possessing an extended consciousness, there is our sense of possessing an autobiographical self, of conscience and of creativity. The possession of an autobiographical self permits humans to construct images of ourself, "who we are physically and mentally, of where we fit socially", the product of continual modelling and remodelling. This dynamic view is far removed from the stasis within which many conventional neurobiological theories of consciousness are embedded.

It is precisely here that I would have liked greater emphasis on the part played by the social in the development of self, but Damasio stays resolutely within the body and within the brain. As a neurologist he sees it as his task, drawing on evolutionary and developmental arguments as well as observations on reductions in consciousness resulting from brain damage, to offer a firmly brain-centred theory, an account of those brain structures that enable or indeed maintain consciousness. Core consciousness, unsurprisingly, is associated with the phylogenetically older parts of the brain, extended consciousness emerges as brain complexity increases, new structures appear and integrative networks of nerves permit greater dynamic interactions. For non-neurobiologists, these sections of the book will undoubtedly make heavy going, despite the wealth of case history with which he supports them, but judicious skipping allows the main lines of the argument to be followed. It is undoubtedly Damasio's emphasis on feelings, on the need for the organism to make sense of and derive meaning from the buzz of informational input its sense organs provide and its memory organises, that is the central thrust of his approach, and that distinguishes it from the overly cognitivist, problem-solving orientation of most other neuroscientists. Consciousness, he concludes, is a revelation of existence and, as it has evolved, has become a means to modify existence.

Damasio has a courteous footnote to McGinn as one of the philosophers who has been engaged in this renaissance of consciousness studies; the compliment is not returned in McGinn's book, and I suspect Damasio's close-grained neurological argument would cut little ice with him. Nonetheless, I have little doubt which approach is likely to prove the most fertile in the coming years, already, if ambitiously, proclaimed by neuroscience as "the decade of the mind".

Steven Rose is director, Brain and Behaviour Research Group, Open University.

The Feeling of What Happens: Body, Emotion and the Making of Consciousness